PowerShell, getting string syntax correct in 7-zip script

Question

I can't seem to solve this, been struggling with it for a while (maybe it's simple; I just can't see it as I've been looking at it for so long). I can get the 7z.exe syntax to work, but when I try and put it together into a simple script, it fails.

e.g., if I run .\zip.ps1 "C:\test\test.zip" "C:\test\test1.txt" "C:\test\test2.txt*

Instead of zipping up the 2 files required, it zips up everything in the C:\test folder, completely ignoring my arguments.

How can I adjust the below string syntax so that 7z.exe will correctly respect the input arguments and compress them from within a PowerShell script?

"Received $($args.Count) files:"
$parent = Split-Path (Split-Path $args[0]) -Leaf
$sevenzip = "C:\Program Files\7-Zip\7z.exe"
$zipname = "$($parent) $(Get-Date -Format 'yyyy_MM_dd HH_mm_ss').zip"
$args_line = $args | foreach-object { "`"$_`"" }
# $args_line = '"' + $($args -join """ """) + '"'   # Want to use """ here so that it can capture not only files with spaces, but files with ' in the filename
''
"Zip Name  : $zipname"
''
"Arguments : $args_line"
''
if (Test-Path $sevenzip) {
    if (Test-Path "C:\0\$zipname") { rm "C:\0\$zipname" -Force }
    ''
    'String output of the line to run:'
    "& ""$sevenzip"" a -r -tzip ""C:\0\$zipname"" $args_line"   # Taking this output and pasting onto console works.
''
    & "$sevenzip" a -r -tzip "C:\0\$zipname" "$args_line"   # This does not work
} else {
    "7z.exe was not found at '$sevenzip', please check and try again"
}

The error that I get is:

Files read from disk: 0
Archive size: 22 bytes (1 KiB)

Scan WARNINGS for files and folders:

1 : The system cannot find the file specified.
----------------

Is this a typo… ```"$zrgs_line"``` that should be ```"$args_line”``` instead? — mclayton, Oct 07 '22 at 13:01
It is, thanks, I've updated it, but I still get errors as above. — YorSubs, Oct 07 '22 at 13:17
You possibly need to specify ```$args_line``` as an array rather than a string as Powershell may be munging your string with additional quotes when it builds the command. Try ```$args_line = $args | foreach-object { “`”$_`”” }``` instead, or even just simply ```$args_line = $args```. I can’t test this myself right now, so it’s a bit of a shot to nothing :-)… — mclayton, Oct 07 '22 at 13:21
still not working unfortunately. Again, if I take the full string as generated on the line before the actual zip, it works perfectly, but the `7z.exe` line inside the script fails every time ... — YorSubs, Oct 07 '22 at 13:28
Either add 7z to the path or run it directly like: `C:\Program\` Files\7-Zip\7z`. Otherwise the & args have to be an array if not spelled out. This is a common question. — js2010, Oct 07 '22 at 15:34

mklement0 · Accepted Answer · 2022-10-07T14:40:30.430

Pass $args directly to your & "$sevenzip" call:

& "$sevenzip" a -r -tzip "C:\0\$zipname" $args

This makes PowerShell pass the array elements as individual arguments, automatically enclosing them in "..." if needed (based on whether they contain spaces).

Using arrays as arguments for external programs is in effect an implicit form of array-based splatting; thus, you could alternatively pass @args.

Generally, note that in direct invocation^[1] you cannot pass multiple arguments to an external program via a single string; that is, something like "$args_line" cannot be expected to work, because it is passed as a single argument to the target program.

If you want to emulate the resulting part of the command line, for display purposes:

($argListForDisplay = $args.ForEach({ ($_, "`"$_`"")[$_ -match ' '] })) -join ' '

Note:

Each argument is conditionally enclosed in "..." - namely based on whether it contains at least one space - and the resulting tokens are joined to form a single, space-separated list (string).
The assumption is that no argument has embedded " chars.

A simplified example:

& {  # an ad-hoc script block that functions like a script or function

  # Construct the argument list *for display*
  $argListForDisplay = $args.ForEach({ ($_, "`"$_`"")[$_ -match ' '] }) -join ' '

  @"
The following is the equivalent of:

  Write-Output $argListForDisplay

"@

 # Pass $args *directly*
 # Simply prints the argument received one by one, each on its own line.
 # Note: With PowerShell-native commands, generally use @args instead (see below). 
 Write-Output $args

} firstArg 'another Arg' lastArg  # sample pass-through arguments

Output:

The following is the equivalent of:

  Write-Output firstArg "another Arg" lastArg

firstArg
another Arg
lastArg

Note: Write-Output is used in lieu of an external program for convenience. Technically, you'd have to use @args instead of $args in order to pass the array elements as individual, positional arguments, but, as stated, this is the default behavior with externals programs. Write-Output, as a PowerShell-native command, receives the array as a whole, as a single argument when $args is used; it just so happens to process that array the same way as if its elements had been passed as individual arguments.

^{[1] You can use a single string as an -ArgumentList value for Start-Process. However, Start-Process is usually the wrong tool for invoking console applications such as 7z.exe - see this answer.}

This is a very useful example for me, as the right way to pass arguments to other programs or cmdlets. I think this will apply to many other situations for some things that I'm doing; thanks for the detailed explanation, much appreciated. — YorSubs, Oct 07 '22 at 15:28

PowerShell, getting string syntax correct in 7-zip script

1 Answers1